1. Field of the Invention
The present invention relates to an apparatus, a method, and a system of measuring a sleep state, which obtain indexes indicating a user's sleep state.
2. Description of the Related Art
Conventionally, a sleep state measuring apparatus that determines a subject's sleep state based on pulse interval data, that is, data set of interval of a subject's pulse wave, and body movement data exhibiting the subject's body movement has been researched and developed. As compared with a large-sized apparatus that automatically determines a sleep state based on patterns of biosignals such as brain waves, eye movement, electromyogram, electrocardiogram, and the like, called a sleep polygraph, the sleep state measuring apparatus has received attention as a sleep state measuring apparatus that is capable of easily determining a sleep state on a daily life.
The sleep state measuring apparatus considers a pulsating interval of heart beats, that is, an activity of an autonomic nerve during sleep, as a pulse interval of a pulse wave so as to determine a sleep state based on an autonomic nerve index obtained from fluctuation in the pulse interval. For example, because a pulse wave, that is, a change in the bloodstream of blood vessels of hands, changes in synchronization with heart beats, it is possible to obtain a pulsating interval of the heart beats based on a pulse interval of a pulse wave. In the related art, such as JP-A 2002-291710 (KOKAI) and JP-A 7-143972 (KOKAI), a sleep state is determined based on an autonomic nerve index obtained from a frequency spectrum component of pulse wave data. That is, a series of pulse interval data is obtained from pulse wave data and the series of pulse interval data is converted into frequency spectrum distribution. Further, an autonomic nerve index is obtained from values of power spectrums in a low-frequency region (around 0.05 to 0.15 Hz) and a high-frequency region (around 0.15 to 0.4 Hz), which are obtained from the series of pulse interval data converted into the frequency spectrum distribution, thereby determining a sleep state according to the autonomic nerve index. In addition, in the related art, as disclosed in JP-A No. 2002-34955, body movement data in addition to pulse wave data is measured, thereby determining a sleep state, such as awakening, REM sleep, non-REM sleep, arousal during sleeparousal during sleep and the like.
In the related art of the first to third documents, it is possible to determine a sleep state, such as awakening, REM sleep, non-REM sleep, arousal during sleep, and the like. However, despite the fact that an object is to easily measure a sleep state on a daily life, it is only the time series variation of the sleep state that is finally displayed. Further, even though general users refer to the time series variation in the sleep state, it is difficult to determine so-called sleeping quality, for example, whether the users sleep deeply or lightly.
In addition, in order for the user to determine sleeping quality, a sleep state needs to be shown as an index. However, because absolute standard is hard to be set due to a wide variation between individuals, it is difficult to evaluate sleeping quality.